1. Field of the Invention
The present invention relates to a vacuum exhaust system for use in evacuating a processing chamber for advanced products such as semiconductor devices, for example.
2. Description of the Related Art
A conventional arrangement of a vacuum exhaust system used in semiconductor device manufacturing processes to evacuate a processing chamber for carrying out such process as etching and chemical vapor deposition (CVD) of semiconductor wafers is shown in FIG. 8. A main chamber (processing chamber)10 is connected on both sides to auxiliary chambers (load lock chambers) 12a, 12b, for loading and unloading purposes through respective gates 14. Each auxiliary chamber 12a, 12b is isolated from, or open to, the external environment by a gate 15.
The main chamber 10 is connected to a vacuum pump 18 through an exhaust path 16 having a valve 20, and each auxiliary chamber 12a, 12b is connected similarly to a vacuum pump 24 through an exhaust path 22 having a valve 26. It has been customary to use rotary oil pumps for the vacuum pumps 18, 24, but lately, dry pumps are used primarily for this type of work.
In this type of apparatus, in order to access the main chamber 10 while it is under vacuum, loading or unloading of a workpiece into the main chamber 10 requires that an auxiliary chamber 12 be evacuated first, and the gate 14 opened next so as to avoid exposing the main chamber 10 to external atmosphere. This is done to prevent the main chamber 10 and associated piping from contamination as well as to improve productivity by shortening the time for re-starting.
In such conventional systems, a vacuum pump is provided for each chamber to evacuate individual chambers, therefore, working efficiency of each vacuum pump is low. If the number of main chambers 10 is increased in an effort to raise productivity, it leads to a problem that the number of vacuum pumps needs to be increased, leading ultimately to a large size facility and higher running costs. If an attempt is made to shorten the time for evacuating the auxiliary chambers, a higher capacity for each pump is required, thus aggravating the above problems even further.